In general, conventional photometric methods for controlling the level of illumination for cameras can be classified into two categories: external photometric methods that use an additional photoreceiving device located near the camera's lens to measure brightness intensity and “through the lens” (TTL) methods in which the camera has a complex circuit and an additional viewfinder to observe an object. TTL methods are often used in single lens reflex cameras.
When photographing with a flash in a consecutive shooting mode (i.e. taking multiple photos in succession), the conventional methods have problems in that overexposure (when the distance to the subject is short) or underexposure (when the distance to the subject is long) may occur.